This invention relates to an arrangement for the control of valve timing in a combustion engine, especially in a large diesel engine with several cylinders, in which the control of a valve in a cylinder is carried out through a follower member, preferably a roll follower, receiving its guidance from an outer cam surface or cam race of a camshaft or the like.
As used in this specification, the term "large engine" means an engine such as may be employed for example as a main or auxiliary engine in a ship or in a power plant for production of heat and/or electricity.
Changing of the opening and closing times of exhaust valves in a diesel engine at varying running conditions has an advantageous effect on the operation of the engine. By controlling the timing of the valves lower consumption rates of fuel can be achieved and the concentration of harmful emissions in the exhaust gases of the engine can be lowered. Changing of timing may, if necessary, be applied to intake valves as well. It must be possible to exercise control while the engine is running.
Changing the valve timing in accordance with the prior art has been accomplished for example by using two separate camshafts provided with separate follower members, or by using two different cam races on the same camshaft. In the latter case, each cam race may have a follower member of its own or a single follower member may select one or other cam race by axial movement of the follower member. Furthermore, according to the prior art, various mechanical lever arrangements and eccentric shafts have been used. Also it is known to change the rotational position of the camshaft relative to the crankshaft and divide and move cam segments.
Most of these solutions have in common a rather complicated construction resulting in substantial extra costs. The extra members and structures needed for the change of timing also require space.